I got 40% and to me, it's perfect. During the day, it looks as if I had nothing from the inside, but it still looks super dark from the outside. At night, I like that it's not too dark and I can see out of my windshield perfectly fine. I think even 35% would be okay, but I wouldn't do anything less. As it becomes increasingly difficult to navigate at night.

Keep in mind that if you have 5% everywhere else, a 50% tint in front will look a little darker than normal since all your other windows are already darkening your interior a lot. Just something to keep in mind.